you will have to unscrew both and see which line shoots fluid. will only take a sec to figure it out. i want to say on my 4.7 2003 the top hose was the one i cut for the trans cooler. also i used the supplied rubber hose that was supplied with the trans cooler kit.

 

https://dodgeforum.com/forum/1st-gen...oil-lines.html

 

FROM ORIGINAL POST; I got it done,, oddly it turned out that the BOTTOM radiator LINE is pushing fluid into RADIATOR from the tranny.. so I cut the upper and continued to supply the aux-cooler.
(So my findings were the same as HYDROSHOCKERs in the link in red above)

 

that is what i said. you have to cut the top line for it to be the line after radiator going back to the trans.

 

I had the same problem with my cooler lines, 2003 Sierra, but I also own a transmission shop. The truck had 78,000 km on it and they wouldn't cover it at all. The crimps leak at the rad, I see this alot normally I just cut the line flare it and reclamp it with no problems but this truck was not old and under warranty after complaining I just repaired it my self. I will never trust GM and there warranties again. Dodge will be my next truck I've never had a problem with warranty on my jeep, they just fix it.
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2013 MERCEDES BENZ SL-CLASS

 

SL2: yes you did say that,, I just read all the advise and forgot some..
I was bent on assuming fluid coming in the top and flowing to bottom.. thanks Phil